Mechanical indicating current limiter



Feb. 9, 1954 M, LAZAR 2,668,887

MECHANICAL INDICATING CURRENT LIMITER Filed NOV. 14. 1952 Mz'ckaelllhgzpPatented Feb. 9, 1954 UNITED sures Michael: D: Lazai', New York-ivh'ilt-assignor to- Burn'd-y; Engineering! Company-Inez, acorpora tion :of New*Yorls Application Newman- 14, 195'2, Serial'Not 320M53 My inventionrelates to current Iinriter'S and more particulars} t'o' the indicating:v'arietyz Previous efforts have been largely confinedilt)the*"peep'-ho1e'type through' the window of: which the parted fusiblewire of the blown limiter could: be" detected: Shel-'1 construction was"not satisfactory f 111* many circumstances;

In'most installations? the limite'rs' are installed side by sideii'n abox-s The box itselris' usually moufiteu with other 'equipmentl Thesecrowded conditions; plus the fact that th'ere is: usually poor lightingin 1 the 1 area; make it very difficult to detect a blown liiniteri Inadditiomxdetecting a' b'lown umiter becomes immeasurably more' difficult*if "the 'limiter 'haippens to' h'ave been blown by a relatively low:current flowing for a long time: 'lli'ese conditions will causeaveryismall section of thefusiiztle wire to melt without the discoloringexplosion-or arcing wh ich' would-make foreasier detection;

Another phase of the problem is i the need for completely covering thefusible wire: and filling the limiter chamber with: roc'kwool quartzgeor some such suitable:material; This is to quench the a'rc and suppressthezusuai explosion; which occurs when the limiter blows under very:high current; Thesuppressing: material=,-. however; interferes withvisual indication: of the fuse condition.

ficcording1y-,uthe principal object of myrinventionto provide: anexplosion-proof.- limiter which is not dependent uponpeep-hole's; ordis"- coloration for" indicating? itscondition.

Gther: objects are: to provide such a limiter thatz is:- light weight:and suitable: foraircraft where excess weight= means a diminished fuelcapacity; to-provide a limiter which will-possess the: same operating;characteristics at elevations of: 50;000feet--as i it does at sea-level;to provide aelimiter with operatingcharacteristics that-wi11 permit acontrolled: heat dissipation to allow certain overloading. faults to becleared; to provide a limiter;that will permit its condition to beindicated by touch to permit ready detection in -dark -areasr. toprovide an' indicating lirr'iit'er the-fuse ofwhich can-beimhedded in'a're'suppression material; and to provide an-indicatinglimiter-havingthe foregoing characteristics which is sma-ll of sturdyconstruction,relativel"? in"- expensive and capable of being,massproducedf v I accomplish these and'other objects 'and ob tainmy. newresults as-will be-apparent'iromthe device described in the following"specification, particularly pointed out 'irf'the claims; andmustratedsin the accompanying drawing, in" which:

Fig; lis a front elvatioifo'ithe"indicating r'espectiv nous; g adjacentthe indicator illustrating a n iedifiaitiblf thereon I aceomplis'h thevariousobj cots: of myinvennew by providing a limiter Illhaving: aplunger H whicli' ex'ternally projected;- as shown in Fig- 5 1 when thelimiter is -blowni Thus-the condition of the limiter can be detectedboth visually and by touch. n

The operating: mechanism: is contained in a housing comprising: twohalves-I 2- and l 2a made of insulating atid fire resisting materialmolded into thedesired shape; V

The housingi half 12 is provided I with a fuse chamber 1 3; and anindicator containing cham- Her it for housing: the fuse assembly- I5 andthe indicaton assembly: I 8, respectively.- x

The fu'seassembly l5-- comprises: two bladespreferablyU-shaped-piecesofsheet metal 11 and I8, folded overan end ofthe fuse wire l9. The indicator assembly i6--com-prise s-two metalcontacts: 20 and-- 2+ preferably made; of fol dd over pieces of sheet Amaterial to each? of-' which is attached one-end of a wire 22 made ofhigh resistance metal suchas Nichi'ome. The" Nichrome wire '22 isofsufiicient length'ahd'sti'ength to hold a coiled spring 23 compressedintermediate two insulating washers 23d positioned adjacent to thetwocoiitacts2'0" and" 2i: The plunger! 1 "forming the-indicator;extends'thro'ugh the coiled" pr ng 23' and abutsthe contact 2-1 at" oneendwhilethe other-'end-is securely fastened to the contact 20; theNichron'ie wire- 22? extending alongside 1 the plunger and secured a'tone' en'd to the: plunger andcontact 2fl a'nd to the othen endlbycontact 2 I; if made discontinuous as shown in Fig.- 2, permits thecoiled springs 23- to drive the plunger and connected contactaway) fromthe remaining contact; The two contacts are prevented mm e'scaping fromtheindicating" chamber" by?" the housingsbarrier 24' and 'itscorresponding barrier 24?: in-the' half I211. The plunger llf is";posttion'ed, however; in themoutlrfi oftlie barrier 24 through which it"outwardly"moves"for afdi's t'ance equal to" the" movement of contact"2' the chamber lfl u'ndr propulsion ot slirifig 2 vTofjreduce"the"cost"of manuraeburegthe housl 2-ma'y-becoiistructedideirtic'cally'- tt half l2a. By providing interlocking symmetry to eachside about axis AA, the pattern is furnished for the mating of the twoidentical parts. Thus the post of housing half l2a, corresponding topost 25, fits into the post hole 21, to center and give lateralsecurement to the two halves i2 and 12a. Similarly the counterpart ridge28a in the opposing half 12a of ridge 28 encircling one half the marginof the fuse chamber I3 is seated in groove 29 forming the remainder ofthe periphery.

Recesses 3G and 3! are provided in the housing for the fuse blades iland I8 respectively, and recesses 32 and 33 form pockets for connectingcontact springs 34 and 35 which electrically connect blade I? to the endof Nichrome Wire 22 at its contact 20, and blade l8 to contact 2|respectively.

The blades may be notched at 35 to fit tongue 3'! of the housing tointerlock the parts, and prevent accidental movement which might affectthe fuse wire l9.

In assembling the parts, the fuse chamber 13 is filled with the arcquenching and explosion suppressing materiallQa, as for instancerockwool, and the grooves 29 and 29a filled with any suitable cementwhich will caus the two halves to be sealed and securely cemented, whenproperly applied to each other. The indicator chamber M may be filledwith a silicon heat resisting grease which will permit a seal of theparts dur ing movement when the Nichrome wire is blown. The silicongrease ma be obtained from Dow Corning Corporation under the designationD04.

Thus when the two matinghalves i2 and We are secured together, thelimiter is sealed from the outside atmosphere, even in the indicatorchamber, and will retain at all times its normal atmosphericcharacteristics until blown.

The limiter is externally shaped to provide finger grips 38. The limiterwhen blown will cause the plunger to project through one of the fingergrips, interfering with its function, as is shown in Fig. 1. Thus thelimiter may indicat its con- I dition simply by placing the fingers onthe grips. Below the finger grips insulating barriers 39 of the housingextend alongside one edge of the blades to prevent accidental contactwith the current during installation. The housing may be externallybridged as at 40 to accommodate the fuse chamber Without weakening thewall thereof.

The plunger may be made of insulating material that can accept afluorescent red dye to facilitate visual inspection.

Finally a plug il may be cemented in the mouth a of the counterpart halfafter insertion of the silicon grease into the indicator chamber M toseal the chamber.

In operation, the limiter is inserted into a standard base where theblades make contact with spring clips of well-known construction and notshown here. The current flowsfrom .blade to blade, through the fuse wiremade of relatively low resistance material such as silver. The fusibleelement is designed to melt when a certain combination of currentintensity and time of fiow is reached in the circuit, which, ifcontinued .longer would endanger the circuit. If the path of leastresistance is broken, the current will be shunted through contactsprings 34 and to the Nichrome wire which being of high resistance willinstantly release spring 23. This action causes the projection ofplunger II to the outside of fin- 4 ger grip 38 and through mouth 25, asis shown in Fig. 2.

The plunger does not interfere with removal of the limiter for it isresiliently held in position by the spring 23 which will be recompressedto permit the plunger to be pushed back in its chamber upon fingeringthe grips 38.

In Fig. 4, I have provided a protective sealing cover for the plungerwhereby a flexible mem-- brane ii: sealed as at 43 to the housing "i4 isoutwardly positioned when the plunger 15 is released by the spring notshown. The usual cement may be used to seal off the parts, allowing theflexible but non-permeable plastic membrane to be outwardly driven bythe plunger to furnish the desired indication, as shown by the dot-dashlines.

In the foregoing specifications I have described I an explosion-prooflimiter which is not dependent upon transparent walls to permit itscondition to be detected.

My limiter is exceptionally easy to assemble for the indicator forms asub-assembly and with the blade and fuse sub-assembly enables the fewparts to be quickly installed in manufacture.

The use of silicon grease enables me to seal off the moving parts whenthe Nichrome wire melts, thus reducing the fire hazard and maintaininthe electrical characteristics of the limiter.

When a battery of my limiters are placed in stack formation, by runningones finger alongside the grips, the blown fuse may be instantly locatedeven in a darkened fuse box.

I have thus described my invention, but I desire it understood that itis not confined to the particular forms or uses shown and described, thesame being merely illustrative, and that the invention may be carriedout in other ways without departing from the spirit of my invention,and, therefore, I claim broadly the right to employ all equivalentinstrumentalities coming within the scope of the appended claims, and bymeans of which, objects of my invention are attained and new resultsaccomplished, as it is obvious that the particular embodiments hereinshown and described are only some of the many that can be employed toattain these objects and accomplish these results.

I claim:

1. In a current indicating limiter comprising ahousing, a pair ofconnecting members having outside contacts, a fuse connected thereto,and a chamber for said fuse; an indicator chamber positioned outside ofsaid fuse chamber, conducting means positioned outside the fuse chamberfor shunting the current from the connecting members to the indicatorchamber, a plunger for movement outside the limiter, means operated bysaid shunt current for actuating the plunger whereby an externalindication will be produced when the limiter has been blown.

2. In the current limiter of claim 1, wherein the housing is providedwith finger grips, and means for allowing the plunger to emerge from thehousing so as to interfere with the finger grip.

3. In the current limiter of claim 1, wherein the connecting members areprovided with longitudinally extending fuse blades, and the housing isprovided with longitudinally extending finger grips for enabling thelimiter to be handled with the fingers, said housing having insulationbarriers positioned between the finger grips and the blades to preventaccidental contact therewith.

the current limiter of claim 1, wherein the housing is made of twoidentical parts, and contains the fuse and indicator chambers, saidparts having interlocking means adapted to be cemented to each other.

5. In the current limiter of claim 1, wherein the housing contains bothfuse chamber and indicator chamber each of which is provided with a sealto prevent escape of the heated contents of the chambers.

6. In the current limiter of claim 1, wherein the means for actuatingthe plunger comprises a spring in the indicator chamber, and a wirehaving a higher resistance than the fuse, for releasing the spring.

7. In the current limiter of claim 5, wherein the indicating chamber isprovided with two openings, one for the plunger and the other forfilling the chamber with a sealing material.

8. In the current limiter 01 claim 5, wherein the indicating chamber issealed with a silicon rease.

9. In the current limiter of claim 6, a unitary assembly consisting ofthe plunger, th spring and the wire.

MICHAEL D. LAZAR.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,343,224 Powell Feb. 29, 1944 2,421,658 Strang et a1 June 3,1947 FOREIGN PATENTS Number Country Date 706,243 France Mar. 24, 1931

